Methods for the production of molded plastic products, which are useful for example for automotive body panels, are well known in the art. Typically, such molded plastic automotive components may be manufactured by reactive molding processes, such as for example "reaction injection molding" (RIM) in which a polyisocyanate, a polyol and a chain extender are brought together in a simple operation (the polyol and chain extender may be preblended if desired) and immediately injected into a mold cavity. Other polymeric materials, such as for example polyesters, epoxies, and polyamides, may likewise be utilized in RIM-type reactive molding processes, and other molding processes, such as for example bulk molding, may be used to form the molded plastic products. The highly reactive liquid starting materials (polymeric precursors) are injected into the mold, generally after having been mixed in what is commonly known as a "positively controlled mixing head".
Reaction injection molded polyurethanes are disclosed in British Pat. No. 1,534,258 and German Auslegeschrift No. 1,196,864, U.S. Pat. No. 3,655,597 discloses reacting polyisocyanate, polyol, blowing agent, diamine and catalyst for the manufacture of molded polyurethane components. A detailed description of the RIM process may be found in Prepelka and Wharton "Reaction Injection Molding in the Automotive Industry." Journal of Cellular Plastics, vol. II. no. 2, 1975. The RIM process has also been advantageously employed in the so-called "encapsulated automotive glazing" manufacturing process, wherein a polyurethane gasket is formed around the perimeter of a glazing unit of transparent material such as glass. See U.S. Pat. No. 4,561,625. Polyester resins and epoxy resins generally useful for reactive molding processes are disclosed in U.S. Pat. Nos. 4,405,538 and 4,581,393, respectively. Reactive molding processes employing polyamides are generally disclosed in the "Kirk-Othmer Concise Encyclopedia of Chemical Technology", John Wiley & Sons, New York, pp. 915-920 (1985).
The reactive molding process may suitably employ any flowable polymeric precursor materials which may be injected into a mold cavity where the polymeric materials react in situ to prepare the desired plastic product. Polyurethane precursors are typically used for the production of rigid automotive components such as bumpers, and for the production of flexible body parts generally known in the motor industry as "soft face elements".
The molded plastic products described hereinabove may be susceptible to degradation upon extended exposure to the environment, particularly the effects of ultraviolet radiation resulting from prolonged exposure to sunlight. In order to minimize the possible deleterious effects of such exposure it is generally necessary to provide the surfaces of the molded plastic components which are to be exposed to the environment, particularly those surfaces which are to be exposed to sunlight, with a protective coating. To that end, exposed surfaces of molded plastic components have heretofore generally been coated with a weather-stable paint which protects the molded plastic component from the effects of ultraviolet radiation. This procedure, of post painting the surfaces of plastic components following the molding process, involves substantial processing costs. Other methods of applying a protective coating, such as for example in-mold coating, likewise increase processing costs in other ways. Finally, post-molding applied protective paint is attached to the molded plastic component by means of mechanical adhesion, which makes the paint susceptible to chipping and pealing where the mechanical bond fails.